The present invention relates to a reset data creation mechanism for a photoconductive drum of an imaging apparatus for forming an image on a recording paper by using an electrophotographic method, by which reset data, obtained when the photoconductive drum is replaced, is supplied to a counter for counting data output in synchronism with the operation of the photoconductive drum having an outside peripheral surface composed of a photoconductive material.
An imaging apparatus (so-called printer) provides a hard copy by printing or drawing data output from a computer, word processor, facsimile and the like on a recording paper by making use of an electrophotographic method.
In the electrophotographic process, the photoconductive material on the surface of a photoconductive drum is uniformly charged and then exposed to form a latent image from which electric charges are removed. The latent image is converted to a toner image by being adhered with toner. The toner image is transferred onto a recording paper and further fixed to the recording paper by a fixing unit.
In the imaging apparatus employing the electrophotographic process, occurrences of phenomena such as insufficient charging, the occurrence of after images remaining on the surface of the photoconductive drum, and the like, increase with the wear of a photoconductive material on the surface of the photoconductive drum and the degradation of the electrostatic characteristics of the photoconductive material caused by the repeated use of the photoconductive material which result from respective electrophotographic processes such as a transfer of images, cleaning of the surface of the photoconductive drum and the like, and thus an insufficient printing (insufficient transfer of image onto a recording paper) and the like are caused by these phenomena.
To cope with this problem, the photoconductive drum is arranged as an easily replaceable unit (photoconductive drum unit) and the number of operations of the photoconductive drum is recorded. When the number of operations exceeds a preset number, an operator is prompted to replace the photoconductive drum.
More specifically, a counter is provided to count pulse signals output in synchronism with the rotation of the photoconductive drum and a timing at which the photoconductive drum is to be replaced is determined based on a count value of the counter. Thus when the count value of the counter reaches a preset value (that is, when the preset number of images has been formed), the photoconductive drum is replaced. The counter must be cleared (reset) when a photoconductive drum in use is replaced with a new one, and for this purpose, for example, a switch means such as a microswitch or the like is provided with the main body of the apparatus to sense the presence of a photoconductive drum and the counter is reset in response to a charge of a sensed signal (sensing-not sensing-sensing) output from the switch means when the photoconductive drum is replaced. Note that when the switch means is arranged to sense a switching member which is swung by the installation of a photoconductive drum unit, the counter can be arranged to be reset by a change of signal of not sensing-sensing-not sensing. Further, the switch means may be arranged such that either the presence or absence of a signal output therefrom corresponds to sensing or not sensing.
With the above conventional arrangement, however, a problem arises in that when a photoconductive drum unit is removed once for the maintenance of the apparatus rather than the replacement thereof, and then mounted again, the counter is reset regardless of that the photoconductive drum has not been replaced, and thus the count is disturbed. Therefore, there is a need for an arrangement wherein a counting is not reset when the photoconductive drum unit is removed for such a purpose (e.g., maintenance) and the replaced.